whitespace-stripping

The following patches fix one (probably rare) bug in

        git apply --whitespace=strip

and then teach it to also complain about initial consecutive spaces that
could be tabs.

The latter is the standard for the kernel, but may not be appropriate
for other projects.  I'd like to make the whitespace code handle the
kernel style completely first, then consider configuration to handle
other styles if people complain.  But maybe the change of behavior would
be an unpleasant surprise for someone with apply.whitespace=strip and a
project that always uses spaces for indents.

--b.